Management of Freshwater Fisheries: Addressing Habitat, People and Fishes

CHAPTER 6.3 Management of freshwater fisheries: addressing habitat, people and fishes

Robert Arlinghaus1,2, Kai Lorenzen3, Brett M. Johnson4, Steven J. Cooke5 and Ian G. Cowx6 1 Department of Biology and Ecology of Fishes, Leibniz‐Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany 2 Faculty of Life Sciences, Humboldt‐Universität zu Berlin, Berlin, Germany 3 Fisheries and Aquatic Sciences, School of Forest Resources and Conservation, University of Florida, Gainesville, USA 4 Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, USA 5 Fish Ecology and Conservation Physiology Laboratory, Institute of Environmental Science and Department of Biology, Carleton University, Ottawa, Canada 6 Hull International Fisheries Institute, Department of Biological Sciences, The University of Hull, Kingston‐upon‐Hull, UK

Abstract: This chapter describes approaches to the management of habitat, people and fish stocks that make up freshwater fisheries. Habitat management is advisable whenever habitat bottlenecks limit the productivity of a fishery. Harvest regulations are a useful conservation strategy when fishing mortality is high or specific sizes of fish are to be protected. Finally, stocking may be useful in situations where natural recruitment is lacking or extirpated species are to be restored. Planning of interventions necessitates a rigorous approach based on principles of adaptive management and structured decision‐making. Given the many stakeholders affected by fisheries management measures in fresh water, an integrative, stakeholder‐inclusive approach is recommended. Keywords: angler, habitat management, harvest regulation, inland fisheries, stocking, minimum‐size limit

Introduction Directive). Reviewing this massive literature is beyond the scope of this chapter. Instead, we focus on the core inland fisheries Similar to commercial marine fisheries, exploitation of management tools and approaches that are chosen to manage, freshwater fish stocks can lead to population declines and alter directly or indirectly, inland fish stocks for fisheries purposes. structural and functional properties and the ecosystem services We do so by acknowledging that in many situations, the main generated by fishes (Holmlund & Hammer, 1999; Allan et al., impacts on freshwater fish stocks lie outside the control of the 2005; Lewin et al., 2006). Freshwater ecosystems have also been fishery manager (Arlinghaus et al., 2002) and may demand strongly affected by anthropogenic change stemming from entirely different and more encompassing actions than those damming, habitat simplification for navigation, agriculture, reported here. hydropower, water extraction, acidification, eutrophication, pollution and release of non‐native organisms (Richter et al., 1997a; Dudgeon et al., 2006). As a result, freshwater fishes are Identifying a general fisheries among the most threatened vertebrates worldwide (Freyhof & management strategy Brooks, 2011), which justifies dedicated management interventions and restoration activities to halt the alarming decline. The Fisheries management is the process by which reliable informa- literature on mitigation, rehabilitation and restoration of inland tion is used to achieve management goals and operational waterbodies is rich and diverse (Cowx & Welcomme, 1998; objectives defined for fisheries resources. Overarching manage- Welcomme, 2001; Cooke et al., 2005). Although most actions of ment goals for inland fisheries include (1) biologically aquatic ecosystem management will also affect fish populations, sustainable use of freshwater fish stocks, (2) conservation of they are usually motivated by a broader environmental aquatic biodiversity and (3) equitable sharing of benefits among framework, also in legal terms (e.g. European Water Framework stakeholders (Welcomme, 2001). Within these well‐accepted

557 558 Fisheries development

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Adaptive &% ##ed management ' # decision making '

Evaluate, adjust Objectives valuate success ather stakeholder input earn esolve conficts djust management actions et objectives, rence points

Implement, monitor Alternatives mplement management plan % "s onduct outreach, education onstruct models, uncertainties easure outcomes redict outcomes, tr s

e hoose management action esign monitoring plan omplete management plan

Figure 6.3.1 The inland fisheries management process formulated for structured decision‐making and adaptive management. Note that the appropriate mix of management actions is decided in the ‘decision box’, which are then implemented and monitored for outcomes (Source: FAO (2012). Reproduced with permission of FAO). goals, a considerable challenge revolves around the need to general management strategy may prove useful given the bio- trade off diverse stakeholder values and to translate these into logical properties of the target fish population (FAO, 2012) is operational management objectives (Fenichel et al., 2013). given in Fig. 6.3.2. These strategies are directed at three key Unfortunately, many usually smaller inland fisheries are not dimensions of inland fisheries: (1) the habitat, which usually economically important enough to justify costly monitoring transcends the aquatic–terrestrial interface; (2) the biota, and management systems (Post et al., 2002). Hence, even if including but not limited to the target fish population; (3) the operational objectives are found, many inland fisheries require humans involved in the fishery (Welcomme, 2001). Deciding on data‐poor or even data‐less management systems (Arlinghaus & an appropriate strategy depends on objectives, the co nditions of Krause, 2013). the ecosystem, non‐fishing impacts and the current fishing Notwithstanding availability of timely and accurate data, the mortality, natural mortality, growth and recruitment rate of the process of inland fisheries management should employ a exploited fish population (Fig. 6.3.2). For example, when the transparent and inclusive approach to achieving management objective is to increase catch rates from an overfished situation, goals and objectives. Because of the complexity of most inland harvest regulations may be advisable (Fig. 6.3.2). By contrast, fisheries and the uncertainty as to how particular policies func- low recruitment of a target species at low fishing mortality may tion, it is advisable to follow an adaptive management approach call upon habitat enhancement or stocking as appropriate tools that is designed to learn from past experiences (Fig. 6.3.1). This to contemplate (Fig. 6.3.2). requires a cyclic process to help sort among competing management actions and find those that best suit the particular objectives and social–ecological conditions of the fishery. An Managing habitat adaptive management approach can either be passive or deliberately active (Walters, 1986) but has to involve stakeholders Purpose of habitat management proactively and follow a structured decision‐making process Alteration and loss of habitat as a result of non‐fishing‐related (Irwin et al., 2011). This chapter will focus on the various anthropogenic activities are major threats to freshwater fisheries management tools that may be chosen as experimental inter- (Richter et al., 1997a) and on global scale have had greater impact ventions to explore within an adaptive management process. on fish communities than inland fishing (Arlinghaus et al., 2002). Inland fishers commonly desire improvements in the catch It is thus not surprising that habitat management is the focus of rate, size of catch or opportunity for harvest. The manager must many management initiatives ranging from policies that protect then confirm or diagnose causes behind reported inadequacies habitat to various enhancement and restoration techniques. in the fishery and choose an appropriate course of action Fisheries managers turn to habitat management where there is a to achieve objectives. A simple decision tree to identify which bottleneck that limits a critical life stage and the productivity of Management of freshwater fisheries: addressing habitat, people and fishes 559

LOW Fishing HIGH mortality?

HIGH Natural LOW mortality? HIGH Natural LOW mortality? 5. Enhance HIGH LOW Growth rate? habitat 1. Encourage LOW Growth HIGH harvest, enhance rate? habitat 6. Enhance habitat HIGH LOW Recruitment? 2. Monitor Harvest limits less useful

3. Encourage 4. Enhance habitat, harvest stock

Harvest limits not useful HIGH LOW Recruitment?

Carrying Carrying capacity, indirect capacity, indirect Legend effects effects Decision point/ population status query Evaluate additional 7. Harvest 8. Enhance habitat, information limits stock, Suggested management action harvest limits Harvest limits useful

Figure 6.3.2 Generalized decision tree for inland fisheries management. An implicit assumption is that the management objective is to increase size and abundance of the target species within ecological limits of the system. A key decision node among general management strategies is the knowledge of the current levels of fishing mortality and whether fishing is considered excessive. When fishing mortality is low (1–4), harvest regulations would not be useful; rather, it may be advantageous to encourage harvest to alleviate potential issues with density‐dependent growth or natural mortality (1 and 3). If fishing mortality is low but availability of fishes not considered high enough for the potential of the waterbody, habitat enhancement might prove very useful (4). This strategy might be complemented by conservation‐oriented stocking to boost recruitment (4). When fishing mortality is high but natural mortality is also high (5) or growth of fishes is low (6), habitat improvements rather than harvest restrictions would similarly be indicated. The manager stands to make the greatest improvements to the fishery with harvest regulations when fishing mortality is high, natural mortality is low, and growth is high (7 and 8). It is only then that harvest limits can increase biomass and size structure of the target population. When natural recruitment is low, harvest regulations might be supplemented by habitat enhancement and stocking (4, 8) (Source: Adapted from FAO (2012). Reproduced with permission of FAO. target species (Fig. 6.3.3) (Cowx & Welcomme, 1998; Bain & not all freshwater habitats can be protected from alteration in Stevenson, 1999). The bottleneck can arise from many sources, light of societal trade‐offs and priorities (e.g. for flood control or from insufficient spawning habitat through disruption to lateral hydropower), so alternative approaches are often explored. and longitudinal connectivity to bottlenecks in the juvenile rear- Most contemporary efforts of habitat management focus less on ing stage and loss of habitat diversity (Fig. 6.3.3). Conceptually, restoration (i.e. attempting to reach a historical state) per se in the structure and function of habitat provide an upper bound on favour of rehabilitation (i.e. attempting to achieve some elements the stock–recruitment curve and also affect the slope of this curve of a past state) or enhancement (i.e. improvements over existing (Hayes et al., 1996). By modifying habitat, fisheries managers can conditions). Mitigation is focused on refining development attempt to increase the slope and hence the productivity of plans for fresh waters such that their impact on fish habitat is exploited stocks (Walters & Martell, 2004). Also, managers may minimized (Cowx & Welcomme, 1998). An example includes attempt to alter the asymptote (i.e. the c arrying capacity) of a installation of fish passage devices at newly constructed barriers stock–recruitment curve. Habitat management may also be used in river ecosystems. Compensation is different in that it recog- to conserve threatened species. nizes that habitat alterations are inevitable and requires that the Given the fundamental role of habitat in supporting freshwa- user of ecosystems compensates for the loss in habitat. Examples ter fish populations and fisheries, protection of habitat from include installation of artificial reefs, constructed wetlands or ongoing anthropogenic change is of primary concern. Obviously, other fish habitat structures (Rubec & Hanson, 2009) or the 560 Fisheries development

Growth habitat Daily activity area Spawning habitat Refuge Feeding

Daily journeys

Larvae Daily activity area

Connectivity Refuge Feeding

Daily journeys

Wintering Juveniles habitat Daily activity area Daily activity area Refuge Feeding Refuge Feeding Daily journeys Daily journeys

Figure 6.3.3 Functional habitat units for fishes (Source: Adapted from Cowx & Welcomme, 1998). building of hatcheries for stocking. Having strong habitat cross‐scale effects, managing habitat is often as much art as protection policy is obviously a prerequisite for applying the science (Van Diggelen et al., 2001). Every year, millions are concepts of mitigation and compensation in a regulatory frame- spent on habitat restoration activities that fail to address the work. Even when such regulations exist, there is evidence that underlying problem that is limiting productivity (Miller & mitigation and compensation activities are not always effective. Hobbs, 2007). In some cases, habitat management may not be An audit of fish habitat compensation projects in Canadian the best tool for the job (Fig. 6.3.2). Often, there are also severe freshwater systems, for example, revealed that although there budgetary and institutional constraints that prohibit engaging were reasonable attempts to replicate structural elements of fish in large‐scale habitat restoration activities (Cowx & Welcomme, habitat, function (as measured by a reduction in productive 1998). The Society for Ecological Restoration developed a series capacity of fish habitat) was reduced in 63% of the compensated of guidelines intended to assist practitioners in establishing the sites relative to the altered habitat prior to its alteration (Quigley & processes needed to engage in effective habitat management, Harper, 2006). Also, there is ample evidence that stocking can which serves as a suitable starting point for anyone considering rarely compensate for severe habitat loss (Walters & Martell, a habitat management project (Clewell et al., 2000). Further 2004) and hence must always be seen as a measure of last resort. planning guidelines, particularly for river restoration and Such examples emphasize that habitat protection for productive rehabilitation, can be found in Cowx and Welcomme (1998), fisheries is more desirable than mitigation or compensation Welcomme (2001) and Roni et al. (2002). whenever socio‐economically feasible. For habitat management to be effective, one must consider Common habitat management techniques both structure and function (Hobbs & Harris, 2001). Habitat There is a wide range of habitat management approaches management, however, often fails to address the functional available for lotic and lentic fresh waters. Some focus more on outcomes and instead focuses on enhancing structure (Quigley & addressing fisheries‐related issues, while others are focused more Harper, 2006). Managing for structure is certainly easier, and on biodiversity, ecosystem health and environmental quality. We metrics of success are often straightforward (e.g. area of habitat primarily describe habitat management techniques that have the restored, number of rocks added to river and number of trees potential to address a limitation or constraint on fisheries pro- planted in riparian zones). By contrast, the function of habitat ductivity (Table 6.3.1). We direct readers to a rich literature on (e.g. nutrient cycling and recruitment) is more difficult to habitat management and ecological restoration in general monitor but is the critical factor for ensuring success of habitat (Hobbs & Norton, 1996; Falk et al., 2006) and more s pecifically management actions. for wetlands (Zedler, 2000), lakes and reservoirs (Olem & Flock, Habitat management is often popular among fishers because 1990; Cooke et al., 2005), large rivers (Cowx & Welcomme, it is an obvious way of improving a fishery (Arlinghaus & 1998), small streams (Hunter, 1991; Roni & Beechie, 2012) and Mehner, 2003; Hickley et al., 2004), but due to non‐linear and catchments (Frissell & Ralph, 1998; Roni & Beechie, 2012). Management of freshwater fisheries: addressing habitat, people and fishes 561

Table 6.3.1 Examples of management actions targeting habitat that may benefit fish populations and their ecosystems

Strategy/goal Explanation and examples

Restore connectivity Install fish passage structures or remove dams to alleviate barriers to fish movement and restore metapopulation dynamics Nutrient abatement Contain point and non‐point sources of excess nutrients in the watershed (often phosphorus and nitrogen) Nutrient supplementation Phosphorus and nitrogen additions to enhance fish production or to compensate for cultural oligotrophication; in some regions, carcasses (e.g. Pacific salmon Oncorhynchus spp.) are added to streams Reduce contaminants Contain point and non‐point sources of contaminants in the watershed (e.g. nitrates, metals and pesticides) Liming Addition of calcium carbonate (limestone or calcite) to neutralize acidified waters Aeration Increase dissolved oxygen concentration through physical means to prevent die‐offs and undesirable chemical dynamics in hypoxic waters (e.g. dissolution of phosphorus and manganese and mercury methylation) Manage turbidity Soil run‐off from the catchment, mixing by boats and bioturbation by fishes can all increase turbidity, limiting photosynthesis and increasing surface temperature; silt control devices or use of buffer zones can reduce turbidity Manipulate flow and water level Mimic natural water level and flow fluctuations in regulated waters; reservoir drawdowns can reduce reproduction of undesirable species; seasonal pulses can be used to stimulate upstream migration of fishes Restore wetlands and estuaries Wetlands provide many ecosystem services including water purification and fish production; constructed wetlands provide opportunities for habitat creation and compensation Erosion control Use of various erosion control structures (e.g. riprap and deflectors) in lentic and lotic systems to stabilize banks and reduce turbidity Restore shoreline and riparian zones Fishes benefit from large woody debris in littoral zones of lentic and lotic systems; excluding livestock protects riparian areas and reduces bank erosion of lotic systems; planting of vegetation Improve spawning habitat Addition of spawning substratum, construction of spawning channels Supplement structure Addition of structural elements that tend to congregate fishes but may not improve ecosystem productivity (e.g. fish aggregating devices and artificial reefs)

Source: FAO (2012). Reproduced with permission of FAO.

Managing habitat in rivers of such activities has been infrequent, precluding an assessment Rivers are subjected to many pressures, which are driven by of success probabilities in large rivers (Roni, 2005). There are, societal requirements for land development, flood protection, however, some examples of where physical structure placement water supply, hydropower generation, waste disposal, recrea- or other large‐scale habitat modifications in large rivers have tional amenities and navigation. These pressures alter transport resulted in improvements in fish productivity (Cowx & of water and sediment, morphology and physical characteristics Welcomme, 1998; see Fig. 6.3.4 for popular actions). As large of the river, and trophic subsidies and interfere with migratory rivers are always downstream of many smaller rivers and they pathways (Poff et al., 1997), all of which can disrupt ecosystem have large catchment areas, a watershed approach to restoration function and affect fisheries yield (Postel et al., 1997). The of large lotic systems is usually preferred (Cowx & Welcomme, expanding field of ecological river rehabilitation endeavours to 1998; Roni & Beechie, 2012). rehabilitate rivers that have suffered anthropogenic disturbances Given the smaller scale of streams and their catchments, by reintroducing habitat diversity while considering the broader physical habitat management activities often result in more landscape, riparian zones, upstream areas and fluvial geomor- immediate results than in larger rivers (Roni et al., 2002). phology (Hobbs et al., 2011). Restoration of streams must include riparian habitats given the importance of shade, woody debris and plants to most stream Management of physical habitat modifications ecosystems (Naiman et al., 2005). Maintenance of buffer strips in lotic systems (Osborne & Kovacic, 1993) and fencing of livestock to exclude The scale of physical habitat management needed to achieve them from streams (Platts & Wagstaff, 1984) represent impor- positive outcomes depends on the size of the system and the tant riparian‐focused management activities. Placement of factors limiting productivity or otherwise contributing to instream structure is common in small streams and is often degraded conditions. In large rivers, creating physical structure done by volunteers or angling clubs (Middleton, 2001). Some is a technological challenge. Channel structure can be modified structures are intended to deflect water to reduce erosion and to improve meander patterns through extensive placement of create riffle–run–pool sequences, while others provide over- boulders and channel profiling (Nagayama et al., 2008). Materials head cover or spawning habitat (Welcomme, 2001). Although such as large woody debris can also be added to increase com- stream restoration occurs on a diversity of systems, certainly the plexity and provide cover for fishes (Fig. 6.3.4). Some researchers most effort has been directed towards salmonids (Hunter, 1991). have questioned whether river restoration can succeed given the Instream habitat enhancement appears most effective when scale at which systems need to be modified (e.g. meanders and employed after restoring natural processes (e.g. provision of connecting backwater areas; Gore & Shields, 1995). Monitoring connectivity and functional riparian system; Roni et al., 2002). 562 Fisheries development

(a) (b)

(e) (f)

Figure 6.3.4 Various restoration strategies including (a) before and (b) after debris removal and structure placement in a stream, (c) before and (d) after dam removal on a stream and (e) construction of habitat structures in a dewatered embayment of a lake and (f) the subsequent planting of endemic vegetation in littoral habitats of a newly created embayment. Management of freshwater fisheries: addressing habitat, people and fishes 563

Despite the valiant effort of volunteers and practitioners and Although dam removal or simply not constructing new millions of pounds of investment on an annual basis, a systematic dams may be of great benefit to riverine ecosystems, the review on the effectiveness of instream structures as a manage- reality is that barriers are important components of modern ment tool to increase salmonid abundance suggested that they society. As such, provision of fish passage devices to enable provide no consistent benefit (Stewart et al., 2009). One of the fishes to move upstream and downstream of barriers is a very reasons underlying the apparent failure of structure placement common mitigation measure and should be a regulatory in increasing salmonid abundance may reflect the lack of requirement for new dams and for relicensing of existing broader programmes addressing the full suite of factors that ones. There are many types of fish passage devices to facilitate constrain productivity (Roni et al., 2002). upstream passage. For example, locks and elevators can be used to lift fish over an obstruction. Fishways are designed to Restoring connectivity in lotic systems dissipate the energy in the water to enable fishes to ascend Habitat connectivity in lotic systems is critical for enabling without undue stress (Clay, 1995). The common types of fishes to move among habitats needed by various life stages. fishways include Denil, vertical slot, pool and weir and Associated with human activities including irrigation, hydro- nature‐like designs (Fig. 6.3.5). Successful implementation of power and recreation, water control structures such as dams and fishways requires a thorough knowledge of the life history, weirs have been installed around the globe. For context, current behaviour and swimming ability of a species (Cooke & Hinch, estimates suggest that there are in excess of 45 × 103 large dams 2013). Successful fish passage also requires that fishes both (primarily for hydropower and flood control) and 800 × 103 locate the entrance to a fishway and then are able to success- small dams (Dynesius & Nilsson, 1994; Rosenberg et al., 2000; fully ascend the device (Bunt et al., 2012). In a recent meta‐ Nilsson et al., 2005). Existing barriers that provide little societal analysis, Bunt et al. (2012) revealed that nature‐like fishways benefit can be removed, but doing so can result in a variety of (e.g. bypass channels with natural sediments; Fig. 6.3.5) had short‐term negative consequences including silt mobilization the highest levels of passage success but generally had poor (Bednarek, 2001). Dam removal is often contentious (Lejon et attraction efficiency. Conversely, conventional constructed al., 2009), but there are an increasing number of success stories fishways (e.g. Denil, vertical slot, pool and weir) had from small streams to large rivers. For example, Burroughs et al. comparatively low passage efficiency but high attraction (2010) reported that the removal of the Stronach Dam on the efficiency. The development of general rules for fish passage Pine River in Michigan resulted in an upstream range expansion is challenging, and there are many examples of failed fishway for eight species formerly found only below the dam. In addi tion, projects. Like other habitat management activities, however, most fish species studied showed an increase in abundance proper monitoring and assessment is rarely conducted, following dam removal. making generalizations difficult (Roscoe & Hinch, 2010).

(a) (b)

Figure 6.3.5 (a) Small nature‐like fishway to facilitate passage at a low‐head dam and (b) a constructed vertical slot fishway at a barrier on a large river. 564 Fisheries development

The science of fishways is continually improving, and what flows can be used to stimulate upstream movement of migratory was once a science based on salmonids now has rich examples fishes (Hasler et al., 2012) or to motivate spawning (Welcomme, from many species and regions (Pavlov, 1989). There is also a 2001). In situations where flow rate is too fast (usually due to movement to question the need for passage as barriers serve as channelization) and young fishes are drifted away, decreased means of restricting invasive species and passage of fishes from releases of flow from upstream control structures may be riverine environments into an upstream lentic reservoir may advisable (Welcomme, 2001). cause an ecological trap (McLaughlin et al., 2013). Downstream passage requires that fishes are provided a safe path avoiding Managing habitat in lakes and reservoirs turbines or other physical damages. As such, various guidance Possibly, the most important pressures acting of lake and strategies including lights, bubble curtains and louvres are reservoir fisheries are linked to water quality and water level per- used to direct fish towards bypass channels or other fish collec- turbations (Moss, 2009) and less to physical habitat modification tion devices (Coutant & Whitney, 2000). Diadromous spe- as in rivers. The quality of water is influenced by pollutants cies including the juvenile life stage of Pacific salmonids including organic wastes, nutrients, metals, poisons, suspended Oncorhynchus spp. and the adult phase of European eel Anguilla solids and cooling water from urban, industrial and agricultural anguilla represent examples for which there is much desire to sources. These drivers can act directly on the fishes, for example, develop effective downstream passage. toxicity of chemicals, or indirectly by changing environmental conditions and consequently the suitability of the habitat for Flow management in rivers fishes, mainly through eutrophication. Slight eutrophication Virtually all lentic ecosystems are controlled by the hydrological arising from organic effluent discharges and run‐off of nutrients regime (Junk et al., 1989). The changing quantity of water f lowing can benefit fisheries through increased production (Hanson & in a river provides habitat and influences water quality, tempera- Leggett, 1982; Stockner et al., 2000). When the nutrient load is ture, nutrient cycling, oxygen availability and the g eomorphic too high and a hypertrophic ecosystem state is reached, however, processes that shape river channels and floodplains (Poff et al., excessive algal and plant growth may lead to reduced fish pro- 1997; Richter et al., 1997b). Natural riverine landscapes (river- duction and loss of fish diversity throughout periods of lethally scapes) are characterized by floodplain, natural flow regime, low dissolved oxygen concentrations, especially in the hypolim- high hydraulic connectivity, a successional l andscape mosaic with nion (Schindler, 2006). Acidification of lakes due to acid dis- high habitat heterogeneity and complex land–water coupling and charge has the opposite effect because its final stage is an almost exchange (Fausch et al., 2002). The shape and size of river channels, dead lake with no decomposition taking place. This type of pol- the distribution of pool–riffle habitats and the stability of the lution is most notable in North Europe and Canada where large substratum are all largely determined by the interaction between numbers of lakes have been affected (Stoddard et al., 1999). the flow regime and local geology and landform (Bunn & Finally, natural fluctuations in water level are a common feature Arthington, 2002). Flow regime is thus a critical factor in deter- of most lakes and reservoirs as a result of seasonal and climatic mining both physical habitat structure and diversity in rivers and variation in rainfall (Ploskey, 1986). The problem is, however, needs to be properly managed. exacerbated in lakes and reservoirs used for water supply and Existing methods for the estimation of environmental flows hydroelectric power generation, which control the water level in differ in input information requirements, types of ecosystems response to supply demand and power generation requirements. they are designed for, time which is needed for their application This drawdown, and the way in which it is achieved, may be and the level of confidence in the final estimates (Hucksdorf disadvantageous to the development of fisheries in reservoirs et al., 2008). The methods range from purely hydrological (Beam, 1983; Ploskey, 1986). The littoral zone can become bar- methods, which derive environmentally acceptable flows from ren, with exposed rock, gravels and sands, reducing the potential flow data and use limited ecological information or eco‐ spawning and nursery areas for many fish species. In particular, hydrological hypotheses, to multidisciplinary, comprehensive the rapid drawdown associated with hydropower generation has methods, which involve expert panel discussions and collection an adverse effect on fishes that spawn in the littoral zone, killing of significant amounts of geomorphological and ecological data eggs and larvae and thus reducing future recruitment to the fish- (Hucksdorf et al., 2008). Dammed rivers often have highly able stocks of these species (Nagrodski et al., 2012). If this is the regulated flow regimes, and rehabilitation requires changes to case, dedicated management interventions to combat pollution dam operations to provide more natural environmental flows and flow are needed. These actions may be complemented with (Welcomme, 2001). In peaking systems with flows that vary on management of structure and refuges in the productive littoral a diel basis relative to hydropower demand, regulators often zones of lakes (Winfield, 2004). prescribe the range of acceptable flows as well as the rate at which flows can be changed (i.e. ramping rates; Smokorowski Managing physical habitat in lentic systems et al., 2011) in an attempt to minimize stranding (Nagrodski Physical habitat modification in lentic systems is not nearly as et al., 2012). In some instances where flows have been modified well developed as a science as for lotic systems. Possible tech- to yield low and stable flows, the use of strategically timed pulse niques include water level management; shoreline development, Management of freshwater fisheries: addressing habitat, people and fishes 565 for example, reinstatement of riparian vegetation and ecotones; avoid unseen pitfalls. The persistence of pollutants and their and creation of artificial or quasi‐natural spawning grounds. transport and cycling mechanisms in the environment are major Water level management essentially controls rapid (diel) water factors affecting the probable success of such measures once level fluctuations to protect breeding habitat for littoral spawn- pollution has occurred (Connell, 1988). ing species. Artificial reefs made up of, for example, old tyres or Even though pollution may not be removed, its adverse woody debris, and replanting of submerged and emergent effects on organisms may be ameliorated by adjusting water vegetation may be appropriate under certain conditions, such as quality. Direct intervention can result in dramatic improve- in small stillwater fisheries (Hickley et al., 2004). Research in ments, such as the aeration and destratification (Ashley, 1985) Wisconsin (United States) has revealed that littoral structural and liming (Clair & Hindar, 2005). These must, however, be complexity, especially in the form of woody debris, is important considered short‐term measures while more permanent pollu- for fish communities in lakes and, when removed, it can have tion control measures are implemented. Natural purification significant detriment to fish populations (Sass et al., 2006). In processes can often provide longer‐term solutions that form reservoirs that are often void of littoral habitat, placement of old part of the pollution control strategy, such as the provision of evergreen fir trees or other woody debris (including placement riparian buffer zones (Osborne & Kovacic, 1993), which help to of half‐log structures) can similarly provide shelter to early life filter the effects of pollutants entering lakes, especially as a result stages of fishes and also improve reproductive success (Hunt & of land use practices. Some pollutants can be removed by Annett, 2002; Wills et al., 2004). Unfortunately, in many smaller harvesting plants and animals, which have absorbed or incorpo- systems, woody debris is removed by anglers in an effort to rated them into their tissues (Susarla et al., 2002). This offers the ‘clean’ shorelines or built angling sites, which may be counter- possibility of using organisms to bioconcentrate pollutants to productive and should be avoided. Placement of o ffshore struc- clean up environments through selective harvesting. tures such as artificial reefs also occurs in fresh water (Bolding et al., 2004), but not nearly as commonly as in marine systems. Flow management and silt deposition in reservoirs In general, use of natural materials (rocks and wood) in In particular, reservoirs suffer from flow‐related habitat freshwater systems is preferable to boats, tyres or other materials disturbances and sediment erosion, transfer and deposition that are often used in marine systems (Seaman & Sprague, resulting from inflow and pulsed flow. Too rapid withdrawal of 1991). Sometimes, structures are placed in systems to aggregate water can cause stranding of fishes and loss of breeding sites and fishes rather than to address a bottleneck, which serves little to eggs attached to marginal bottom substrata, reducing survival increase productivity but may still be a relevant management and reproduction (Welcomme, 2001). Accelerated flooding will technique if it enables better access to fishes. Smokorowski and also destroy rooted vegetation and release sediments. Increased Pratt (2007) conducted a meta‐analysis and emphasized that rate of silt deposition in reservoirs can only be managed through habitat enhancement activities in lakes have inconsistent out- changing land use and control of upstream operations to avoid comes. In general, the scope for physical modification is limited downstream release of sediments. Drawdown or overly rapid in lakes and reservoirs because nutrient level, temperature and filling in reservoirs necessitates the active management of general basis morphology seem to structure lentic fish stocks to discharge patterns during reservoir operations. In some cases, a greater extent than the physical structure of the littoral drawdown can even have positive effect on some trophic layers (Mehner et al., 2005; Brucet et al., 2013). Hence, adding nutri- by exposing prey fishes to predators as the refuges in the littoral ents to smaller waterbodies is a viable enhancement technique zone are lost. Dewatering during spawning time might also be in some regions of the world (Welcomme, 2001). strategically used to control unwanted species that spawn in littoral zones. Managing pollution control, treatment and prevention in lakes and reservoirs Biomanipulation in lentic systems There are many and varied pollution control and prevention In some circumstances, reducing nutrient input into the aquatic methods to reduce the impact and discharge of potentially pol- environment has little effect on water quality. Phosphorus and luting effluents to improve water quality and fisheries in lakes nitrogen locked in the sediments continue to be released over and reservoirs including removal of phosphate from detergents, many years, despite reduced external loading. An alternative which is increasingly being adopted in Europe and America to approach, which has received much attention in the 1980s reduce eutrophication (Hammond, 1971); phasing out the use through to the 1990s, is that of biomanipulation (Shapiro et al., of persistent pesticides (Sun et al., 2006); control of acidic emis- 1975). This approach, instead of concentrating solely on the sions (Schindler, 1988); and diversion of effluents (Beklioglu nutrient source, targets the ecological trophic dynamics as et al., 1999). Diversion of effluents may be desirable to allow one influenced by fishes (Mehner et al., 2004). Several studies have waterbody to be sacrificed for the sake of another; diversion shown that removal of planktivorous fishes can lead to clear may not merely transfer the problem elsewhere if the recipient water, as a result of reduction on predation pressure on the system affords greater dilution or is more resilient in other ways. large‐bodied zooplankton that graze on the phytoplankton This technique, however, needs careful prior assessment to (Kitchell, 1992; Søndergaard et al., 2008). The long‐term success 566 Fisheries development of biomanipulation depends on the external nutrient levels and Types of regulations on continued intervention into a usually resilient system Regulations of harvest and landings are present in almost all (Mehner et al., 2004). inland fisheries and are particularly advisable when fishing mortality is high on otherwise self‐reproducing stocks (Fig. 6.3.2). Regulations can either be input controls (regulating Managing people with regulations the amount and manner of fishing or inputs) or output controls (regulating the fate of the catch and the amount of harvest, the Purpose of regulations output; Morison, 2004), and they can either be formal or infor- Regulations are the most ancient inland fisheries management mal based on social norms and mutually agreed‐upon rules of measures (Hoffmann, 1996). Most inland fisheries regulations behaviour (Cooke et al., 2013). Popular input controls include are promulgated in laws, bye‐laws and official regulations in closed areas, closed seasons, gear restrictions and other forms of public fishing rights systems and are sometimes further access and effort controls, such as licensing. Common output extended by the holder of the fishing rights under private fish- controls include quotas, daily or weekly bag limits, length‐based ing rights systems such as those in Central Europe or by infor- harvest limits and harvest tags, or specifically in recreational mal institutions on a voluntary basis (Cooke et al., 2013). The fisheries harvest bans via total catch‐and‐release policies purposes of most fisheries regulations include managing social (Table 6.3.2). While effort restrictions (e.g. limited entry) are issues (e.g. attempt to distribute harvest more equitably), relatively rare in inland fisheries as compared to marine com- preventing overfishing, maintaining a suitable stock structure, mercial fisheries (Cox & Walters, 2002), managers can use a maintaining fish welfare (for instance by demanding a rapid variety of indirect methods of manipulating the intensity of killing process; FAO, 2012) and manipulating an aquatic com- fishing. For example, requiring licences and fees or avoiding the munity (for example predator–prey interactions) (Arlinghaus development of access roads and boat ramps may prevent some et al., 2002). Many regulations such as quotas or length‐based from participating, and gear restrictions such as fly fishing‐only harvest limits are predominately directed towards selected sections or barbless hooks are frequently used to reduce the commercially valuable or highly appreciated species of the fish appeal and efficiency of recreational fisheries without directly community. Many regulations, however, are not backed up by controlling the amount of fishing effort. controlled, replicated scientific studies but rather set arbitrarily Length‐based harvest limits (Table 6.3.3), daily bag limits and and reflect practical experience (Johnson & Martinez, 1995; annual quotas as output control measures have several purposes Wilde, 1997; Radomski et al., 2001). Because pressure on habi- but are generally used to limit fishing mortality. Daily bag limits tat and fish stocks will continue to intensify, the role of regula- are probably the most common output control measure in rec- tions in inland fisheries management will probably increase in reational fisheries (Isermann & Paukert, 2010). These rules the future (Noble & Jones, 1999). affect the per capita harvest rate and harvest expectations of

Table 6.3.2 Management actions and regulations targeting inland fishers and fish–fisher interactions

Control type Explanation

Input controls Licensing and fees Fees based on duration of licence, species, residency, status (e.g. youth, aged, military, student, native and tourist) Gear restrictions Hook and line, hook type, artificial versus bait, mesh sizes, length of gillnets and type of traps Method restrictions Motor trolling; attractants such as ground baiting, artificial light and scents Closed times, seasons Spawning period, aggregations and stressful environmental conditions Closed areas Spawning areas, aggregations, refuges and protected areas User conveniences Provision of boat landings, fishing piers and fish cleaning stations may attract recreational fishers Effort restrictions Limited entry and number of rods, lures and lines Output controls Length‐based harvest limits Limit size of fishes retained (minimum, maximum, open or closed slot limits and ‘one fish over a given size’ limits) Bag limits or quotas (daily, weekly Limit number of fishes retained, daily or annually, and in possession with tags and stamps as variants for and annual) particular sizes Sale of fishes Prohibit commercialization or trade Harvest restrictions Restrict based on wild versus hatchery or conservation status, sometimes harvest of non‐native fishes is liberalized to conserve native fishes Harvest mandates, bounties Encourage harvest of overabundant or undesirable species Way of killing In some countries, there is a mandate for rapid kill in recreational fisheries for fish welfare reasons

Source: FAO (2012). Reproduced with permission of FAO. In general, input controls regulate the amount and manner of fishing, and output controls regulate the fate of the catch. Management of freshwater fisheries: addressing habitat, people and fishes 567

Table 6.3.3 Five commonly applied length‐based harvest regulations used to manage inland fisheries and the associated vulnerability to harvest, management objectives and demographic conditions necessary for the tool to be effective

Size limit type Fishes that must be released Management objectives Demographic conditions

Minimum Fishes smaller than the size limit Conserve recruits; produce larger fishes for Low recruitment, rapid growth, low M; stocked reproduction and harvest populations Maximum Fishes larger than the size limit Reduce abundance and competition among High recruitment, slow growth, moderate M small fishes; maintain trophies and fecund large spawners Open slot Fish above and below an intermediate Protect young recruits and spawners; Low recruitment, rapid growth, low M; (harvest slot) size class (combination of minimum and maintain yield and CPUE; protect large, particularly useful when size‐dependent maximum‐size limits) fecund spawners, maintain trophies maternal influences affect recruitment and when fishing could deplete the spawning stock Closed slot Fishes within an intermediate size class Reduce abundance and competition; allow High recruitment, slow growth, high M (protected slot) harvest of large fishes Total catch and All fishes Improve CPUE and size, maintain stock in Little interest in harvest by fishers, high F; release ‘natural’ condition, consumption sensitive stock; high contamination prohibitions

Source: FAO (2012). Reproduced with permission of FAO. CPUE, catch per unit of effort; F, fishing mortality; M, natural mortality. people and thus their behaviour (Beard et al., 2003). In many fishing mortality and produce ‘intentional overfishing’ for cases, however, unless bag limits are very restrictive potentially conservation reasons. Such measures may be complemented displacing effort or severely limiting the take, they will not with gillnetting and trawling, installation of non‐passable reduce harvest mortality sustainably because few recreational barriers and in extreme cases uses of chemicals to kill off fishers actually catch the daily limit. In these situations, effort entire waterbodies. Because some fisheries are today based on controls and length‐based limits on harvesting (Table 6.3.3) non‐natives, such draconian measures are prone to much may be more effective for reducing fishing mortality. Effort can stakeholder conflict and demand an inclusive management be controlled by limiting licence sales, and harvest quotas can be process to reach consensus. implemented with season‐long bag limits (e.g. punched cards or Length‐based (alternatively termed size‐based) harvest harvest tags). regulations and limits are another common form of output con- In contrast to marine fisheries, annual quotas are relatively trol, which prescribes the lengths of fishes that may be harvested rare in inland fisheries, which instead focus on a portfolio of and those that must be released (Table 6.3.3). By carefully tailor- alternative measures such as protected seasons, minimum mesh ing length restrictions to match fish population characteristics sizes and length‐based harvest limits, sometimes completed and level of fishing effort in light of objectives, the manager can with partial protected areas where fishing is prohibited. Because also use fishing as a means to manipulate fish population struc- many inland fisheries are managed based on a set of regulations, ture towards desired states. For example, individual growth in it is very difficult to tease apart the relative effect of any given body mass can increase, and productivity can be enhanced by regulation type using observational data. Catch and release will targeting fishing mortality on overabundant size and age classes, be associated with almost all harvest restrictions. In extreme and recruitment can be improved by protecting age and size cases, total catch‐and‐release rules can increase use intensity of classes carrying the most fecundity and the most successful prog- a fishery without depleting the fish population, unless hooking eny (Arlinghaus et al., 2010; Gwinn et al., in press). Minimum‐ mortality exceeds c. 30% (Coggins et al., 2007). The knowledge size limits may be used to prevent growth overfishing and of hooking mortality is hence critical for many fishery managers conserve young fishes when they are relatively rare due to low (Arlinghaus et al., 2007), and in case of undesirable levels, the recruitment (or in stocked populations). In order for a minimum‐ manager may need to restrict tackle or fishing methods to maxi- size limit to be effective, it is necessary that protected fishes have mize survival of released fishes. rapid growth and low natural mortality to allow them to recruit Although in many cases regulations are aimed at limiting to the vulnerable population (Fig. 6.3.6). The manager may also fishing mortality, in some cases, they may be used to maxi- wish to set the minimum‐size limit above the size at maturation mize the take of undesirable fish species. Worldwide large‐ to allow fishes to spawn prior to being vulnerable to harvest. Note bodied non‐native predators are thriving in many waterbodies, that although many fisheries are routinely managed based on many of which were deliberately introduced by anglers minimum‐size limits, there are a range of other tools (e.g. harvest (Johnson et al., 2009). Predation by non‐native fishes can slot length limits or protected slot length limits) that may offer reach very high levels and threatens many native fish popula- better results under particular conditions (Fig. 6.3.6). Particularly tions (Eby et al., 2006). One means of reducing the abundance when trophy fishes are to be maintained and numerical harvest to of the non‐native is to liberalize harvest so as to increase be maximized, minimum‐size limits will not perform well at high 568 Fisheries development

HIGH Fishing LOW mortality?

2. Limits HIGH Natural 1. Limits not useful mortality? not useful

LOW

Density- LOW NO 6. Bag Growth? dependent limits growth?

YES HIGH

NO 3. Closed HIGH Will fshers 7. Limits Recruitment? slot harvest small not useful fshes?

LOW YES

4. Minimum, NO Size-related Harvest of large NO fecundity & 8. Maximum total C&R fsh desired? Ricker S-R?

YES YES

5. Open slot, 9. Closed total C&R slot

Figure 6.3.6 Decision tree for selecting appropriate size and bag limits based on the intensity of fishing, target fish population’s demographic characteristics and fisher desires. When fishing mortality is low (1), harvest restrictions would not provide any benefit. If natural mortality is high (2), then deferring harvest will not result in more large fishes. The manager can expect size and bag limits to have the greatest impact on the number of large fishes when fishing pressure is high and fishes grow quickly and experience low natural mortality (3, 4 and 5). When growth is slow, size limits may be useful for reducing density‐dependent growth depression by channelling harvest onto overabundant size classes (8 and 9). In cases where demographics of the stock are completely unknown, bag limits (6) should be established as a precaution against overharvest. Size‐dependent fecundity means size‐ dependent influences of females on recruitment stemming from fecundity or egg quality influences. C&R, total mandatory catch and release; S–R, stock–recruitment relationship, with the Ricker curve (Ricker, 1954) being a specific one with overcompensation [Source: FAO (2012). Reproduced with permission of FAO]. fishing effort intensities, in which case harvest slots are the supe- population sizes (Wilde, 1997). Based on such results, some have rior regulation (Fig. 6.3.6; Arlinghaus et al., 2010; Pierce, 2010; questioned the general usefulness of minimum‐size limits for eco- Gwinn et al., in press). When fish populations follow a Ricker logical and evolutionary reasons (Conover & Munch, 2002; Law, stock–recruitment function with overcompensation, harvest slot 2007), and increasingly, alternative r egulations are sought, in par- will not only maximize numerical yield as shown by Gwinn et al. ticular when maintaining large fish in the stock is considered (in press), but they will produce maximized biomass yield, some- important (Gwinn et al., in press). In this context, the use of thing that has t raditionally been assumed to be achieved by mini- harvest slots has increasingly been p roposed as alternative to mum length limit regulations (R. Arlinghaus, R. N. M. Ahrends, protect large and old as well as immature fish for reaping e cological M. S. Allen, D. C. Gwinn and C. J. Walters, Unpublished data). (Berkeley et al., 2004; Venturelli et al., 2009; Arlinghaus et al., Despite the frequent use of length‐based harvest limits in nearly 2010), evolutionary (Conover & Munch, 2002; Law, 2007; all inland waterbodies (Radomski et al., 2001), most empirical Matsumura et al., 2011) and fisheries benefits (Jensen, 1981; studies evaluating the effectiveness of such regulations are single‐ Arlinghaus et al., 2010; Gwinn et al., in press). system case studies that lack controls and long time series, and hence have low power to detect regulation effects (Allen & Pine, Informal institutions, enforcement and the human 2000). Using meta‐analysis techniques, Wilde (1997) studied min- dimension imum length limits and protected slot length limits in l argemouth Any non‐compliance of fishers and anglers with regulations and bass Micropterus salmoides fisheries in the United States. He found the resulting illegal harvest will reduce the efficiency of even protected slots to be effective in increasing the proportion of large the best planned fishery regulation (Gigliotti & Taylor, 1990; fish in the stock, but they failed to increase angler catch rates, Sullivan, 2002). Non‐compliance needs to be addressed by which may indicate that they did not elevate stock abundance. appropriate enforcement (Walker et al., 2007) or by development By contrast, minimum length limits elevated catch rates and of appropriate social norms. Although regulations are often Management of freshwater fisheries: addressing habitat, people and fishes 569

formal, there are many opportunities for inland fishers to stocks (Hilborn, 1998; Walters & Martell, 2004). Depending on voluntarily adopt conservation‐minded measures (either as indi- fishery status, fishing mortality and habitat conditions, different viduals or more collectively as part of a fishing club or regional forms of stocking are warranted (Figs 6.3.2 and 6.3.7). In fisher- organization) to help support regulations (e.g. by reducing ies that are close to the natural carrying capacity and productive hooking mortality through appropriate gear choice). Informal potential for the adult stock, stocking is unlikely to provide ben- institutions (rule in use) may make formal regulations superflu- efits and alternative strategies or ‘do nothing’ should be consid- ous (Cooke et al., 2013). For example, in some fisheries, people ered. Stocking for fishery enhancement may be considered when voluntarily release all the fishes captured (Arlinghaus et al., the adult stock is deemed to be below its carrying capacity due to 2007), obviating the need for a restrictive harvest policy to reduce recruitment limitation, a si tuation not uncommon in fish stocks fishing mortality. Alternatively, people’s ‘unexpected’ behaviour even under natural co nditions and often brought about by may render some official regulations ineffective when, for anthropogenic modification of critical juvenile habitat. example, people refrain from harvesting small fishes under a Supplementation may be indicated where populations are very protected slot regulation aimed at reducing density‐dependent low in absolute numbers over extended periods to reduce extinc- competition (Pierce & Tomcko, 1998). tion risk and loss of genetic diversity. Where limiting effects of Regulations should not be too complex or too system specific habitat or overharvest on population abundance and productiv- to reduce the information burden and increase the ease of ity can be ameliorated, stocking may be used to speed up rebuild- communication and acceptability by fishers. Usually, more ing or to reintroduce locally extirpated species. Finally, where novel regulations are initially resisted, unless the benefits anthropogenic habitat change effects are pervasive and cannot become obvious. Regulatory planning must involve a thorough be controlled, the development of culture‐based fisheries where understanding of the fishery’s human dimensions and be com- fishable stocks are supported wholly by stocking is indicated. plemented by professional outreach and communication that is Sometimes, this includes the release of non‐native organisms tailored to the stakeholders. Managers should be aware of the (e.g. rainbow trout Oncorhynchus mykiss in standing waterbod- emergence of voluntary behaviour that arises from education, ies in Central Europe). This practice is known as introduction or outreach and the spread of new social norms, which can assist in transfer of new species or genotypes, which is today seen very sustaining fisheries using a ‘softer approach’ to resource critical in western countries due to potentially pervasive impacts stewardship. Such an approach is particularly effective in devel- on native biodiversity, which can motivate costly ‘clean‐up’ res- oping countries where formal management capacity and toration activities (Johnson et al., 2009). Due to space limita- enforcement are often lacking and fisher communities are often tions, introductions shall not be discussed further in this chapter, closed and hence personal contact intimate. In these situations, and the reader is referred to the wider literature on this topic rule breakers risk reputation loss, which promotes rule compli- (Welcomme, 1988, 2001). All introductions have to follow rigor- ance. Where voluntary behaviour is not enough, Walker et al. ous ecological risk assessments due to potentially irreversible (2007) provide examples of (surprisingly moderate) enforce- and long‐lasting effects in the recipient ecosystems (EIFAC, ment needs to ensure rule compliance in inland fisheries. 1988).

Types of stock enhancement systems Enhancing or restoring fisheries Different management applications call for different enhance- using stocking ment system designs. Lorenzen et al. (2012) identified five major stock enhancement types ranging from primarily Together with measures to reduce unwanted species, stocking production‐oriented systems where the aim is to maximize and introduction are fisheries management measures that production or availability of fishes while minimizing detrimen- directly target fish stocks (Arlinghaus et al., 2002). Fisheries tal impacts on wild populations to conservation‐oriented enhancement or restoration through stocking is mostly based systems where the aim is to conserve or restore wild populations on fishes produced in aquaculture but may also happen via the (Table 6.3.4). (1) Culture‐based fisheries are fisheries that are legal or illegal translocation of wild fishes. largely or entirely dependent on releases of cultured fishes (Welcomme & Bartley, 1998). Most involve species that do not Purpose of stock enhancement using stocking reproduce naturally in the system, which Cowx (1994) described Stocking can generate multiple benefits including increasing as maintenance stocking. Some culture‐based fisheries are stock abundance and fishery yield or opportunity to catch, as stocked to support harvests far in excess of those that could be well as aiding the conservation and restoration of depleted, sustained through natural recruitment and can involve sterile threatened and endangered populations (Lorenzen et al., 2012). hybrids or fishes that have been intentionally sterilized (e.g. While stocking can be used effectively in certain situations, triploid grass carp Ctenopharyngodon idella for vegetation many enhancements have failed to deliver significant increases control; Cassani, 1995). Other culture‐based fisheries and in yield or other social or economic benefits or have had delete- ranching systems use species that are non‐native to the region, rious effects on the naturally recruited components of the target which may be problematic for ecological and social reasons 570 Fisheries development

Assess status of fshery and condition of habitat

Set management objectives

YES Is system at NO Consider stocking carrying for capacity? enhancement

Can habitat Consider stocking NO YES Improve for mitigation, improvement habitat maintenance ameliorate?

Consider stocking NO for restoration

Consider Can harvest NO YES Restrict introduction, regulations harvest put-take stocking ameliorate?

Stocking strategy •Ecological factors • Eco-evolutionary risks •Feasibility • Cost-beneft analysis

REJECT ACCEPT Consider alternative Implement Evaluate stocking strategies or stocking programme do nothing programme

Figure 6.3.7 Outline of a decision tree for planning a stocking programme appropriate to fisheries status and habitat condition (Source: Modified from Cowx, 1994 and FAO, 2012). when released in open waterbodies. Under certain situations, salmon Oncorhynchus spp. enhancements and many smaller for example, put‐and‐take O. mykiss fisheries in small stillwaters initiatives, mostly for recreational fisheries (Welcomme & in Central Europe, the ecological impacts of culture‐based Bartley, 1998; Hilborn & Eggers, 2000). Under certain fisheries with non‐natives may be small. In general, well‐ conditions, stock enhancements can substantially increase planned stocking and harvesting regimes in culture‐based overall abundance of catchable fishes and fisheries yield, but this fisheries can be tailored to meet production objectives with few will almost always involve some level of negative impact on impacts on the wild stock components, often resulting in a the wild population component (Lorenzen, 2005). The challenge population structure that maximizes somatic production and for population management in enhancements therefore is to the abundance of catchable‐sized fishes but is incompatible with achieve combined stock production or abundance targets while sustaining natural recruitment of the target species (Lorenzen, keeping impacts on the wild stock component within acceptable 1995, 2005; also called put‐grow‐and‐take fisheries if juvenile limits. Aquaculture production and genetic management of fishes are released or put‐and‐take when adults are released). stock enhancements normally place great emphasis on produc- Managing impacts on non‐target species and the wider ecosys- ing seed fishes of wild‐like phenotype and genotype, except in tem can be a major consideration, due to the building up of some cases where the stocked population components are inten- populations that are not naturally present in the system and tionally separated from co‐occurring wild components. Because promotion of intensive harvesting that may also affect non‐ stock enhancements aim to increase the abundance of existing target species. (2) Stock enhancement involves the continued stocks, normally to a level that will remain below the unexploited release of hatchery fishes into a wild population, with the aim of abundance of wild stock due to ongoing fishing exploitation, sustaining and improving fisheries in the face of intensive impact on non‐target species and the wider ecosystem tend exploitation or habitat alteration. Stock enhancement is distin- to be of lesser concern than in culture‐based fisheries. (3) guished from culture‐based fisheries and ranching by the Restocking or stock rebuilding involves temporary releases of presence of a naturally recruiting wild population and from the hatchery or wild fishes aimed at rebuilding depleted p opulations more conservation‐oriented approaches of supplementation more quickly than would be achieved by natural recovery. and restocking by its primary focus on fisheries production Restocking from nearby waters is used widely to restore fresh- (Table 6.3.4). Examples of stock enhancements include Alaska water fisheries after pollution events or in conjunction with Management of freshwater fisheries: addressing habitat, people and fishes 571

Table 6.3.4 Typology of enhancement fisheries systems

Culture‐based Fisheries stock Restocking or stock Supplementation and Reintroduction and fisheries enhancement rebuilding captive breeding translocation biomanipulation (integrated or separated programmes)

Aim of management Increase fisheries catch Increase fisheries catch Rebuild depleted wild Reduce extinction risk Re‐establish and naturally recruiting stock to higher and conserve genetic populations in stock abundance diversity in small historical range populations Culture system Domestication type Domesticated, mixed Mixed, wild‐like Wild‐like Wild‐like Wild‐like Developmental Sterility, conditioning Conditioning for natural Conditioning for natural Conditioning for Conditioning for manipulations for natural environment environment, in environment natural environment natural environment and return or recapture separated programmes also for return or recapture, possibly sterility Genetic management Selection for high Integrated programmes: Preserve wild population Preserve wild population Assemble diversity of return to fishing gear as for restocking genetic characteristics genetic characteristics, adaptations or use Separated programmes: maximize effective stocks adapted to selection for high return population size similar habitats and separation of wild and stocked fishes Natural system Release Early stages and Large juveniles, Any life stage, high Any life stage, low Any life stage, juveniles or large moderate–high density density density to supplement low density ‘catchable’ fishes, natural recruitment high density Fishing intensity High Integrated programmes: Low Low Low moderate Separated programmes: high Biological characteristics Cultured species Native or non‐native Native Native Native Native Wild population Usually absent Present (large, but Present (depleted) Present (small, declining) Absent (locally extinct) possibly depleted) Biological interactions Interspecific ecological Intraspecific ecological, Intraspecific ecological, Intraspecific ecological Interspecific ecological genetic genetic and genetic

Source: Adapted from Lorenzen et al. (2012). habitat restoration (Philippart, 1995). Theoretical analyses and 2000; Hilderbrand, 2002). Captive breeding is often part of empirical evidence show that where populations have been supplementation efforts. Population management in supple- depleted by overfishing, a substantial reduction in fishing inten- mentation typically involves only moderate releases to not sity is always required to achieve stock rebuilding (Fig. 6.3.2), depress the wild population component further, stringent and restocking is likely to be effective as an additional measure restrictions on harvesting and auxiliary measures such as habi- only in very depleted populations (Lorenzen, 2005). In restock- tat restoration and control of non‐native species. Genetic ing, release numbers must be substantial relative to the management is focused on maintaining the structure and abundance of the remaining wild stock if rebuilding is to be adaptations of the wild stock and often involves breeding plans significantly accelerated. Aquaculture and genetic management designed to increase the genetically effective population size are clearly focused on maintaining the characteristics of the wild compared to that of the same population under random mat- population. (4) Supplementation is defined here as the contin- ing (Hedrick et al., 2000). Supplementation can mitigate ued release of cultured fishes into very small and declining against extinction from demographic stochasticity and main- populations. Supplementation primarily serves conservation tain or expand genetically effective population size but may aims and specifically addresses threat processes in small and carry short‐ and medium‐term fitness costs (Fraser, 2008; declining populations: demographic stochasticity, loss of genetic McClure et al., 2008). (5) Reintroduction and translocation diversity and Allee effects (Caughley, 1994). Supplementation involve temporary releases of cultured or captured wild fishes has been used most widely in salmonids (Hedrick et al., with the aim of re‐establishing a locally extinct population 572 Fisheries development

(Philippart, 1995). The fishes to be released may have been Table 6.3.5 Elements of the updated responsible approach to fisheries cultured, possibly for multiple g enerations, or may be brought enhancement into captivity only briefly as part of a translocation of Stage I: Initial appraisal and goal setting wild stock. Reintroduction aims at establishing a healthy Understand the role of enhancement within the fishery system population that is genetically adapted to the local en vironment, Engage stakeholders and develop a rigorous decision‐making process self‐sustaining, genetically compatible with neighbouring Quantitatively assess contributions to fisheries management goals Prioritize and select target species and stocks for enhancement populations so that substantial outbreeding depression does Assess economic and social benefits and costs of enhancement not result from straying and interbreeding between populations and sufficiently diverse genetically to accommodate environ- Stage II: Research and technology development including pilot studies Define enhancement system designs mental variability over many decades (Reisenbichler et al., Develop appropriate aquaculture systems 2003). Genetic management of such p rogrammes is parti- Use genetic resource management cularly challenging because unless a representative and suffi- Use disease and health management ciently large sample of the original population has been Ensure that released hatchery fishes can be identified Use an empirical process for defining optimal release strategies brought into captivity prior to its extinction in the wild, the reintroduced population must be assembled from populations Stage III: Operational implementation and adaptive management other than that originally present. Reisenbichler et al. (2003) Devise effective governance arrangements Define a management plan with clear goals and decision rules point out that while it is generally best to adhere to the ances- Assess and manage ecological impacts tral lineages for the species to be restored, establishment suc- Use adaptive management cess is likely to be greatest for fishes from populations adapted to similar environmental conditions, which may not always be Adapted from Lorenzen et al. (2010). those now extant from the lineage that was originally present in the release habitat. Perhaps the majority of culture‐based fisheries rely on stocking of large juveniles or even catchable‐sized fishes, and the key Considerations for successful use of stocking biological processes driving their dynamics are then size in fisheries enhancement and restoration dependence in mortality and density dependence in growth of Key considerations for the use of stocking are outlined in the released fishes. Lorenzen (1995) and Lorenzen et al. (1997) responsible approach to fisheries enhancement (Lorenzen et al., explored the dynamics of such fisheries theoretically and in a 2010). The recent version of the responsible approach divides case study. Key insights were that the overall yield is determined the considerations into three stages, starting from an initial by the combination of stocking density, size at stocking and appraisal of the potential for enhancement to contribute to fishing pressure. The highest yields are achieved when culture‐ fisheries management goals (stage 1) via technology develop- based fisheries are stocked and harvested intensively. New ment and pilot studies (stage 2) to operational implementation biomass production is maximized when fishes are harvested (stage 3) (Table 6.3.5). Here, we summarize key aspects that as late juveniles, soon after the somatic growth is highest, while have to be considered when the approach is implemented into conversely, if large fishes are to be produced, it limits the overall the practice of stocking. biomass production that can be achieved. In put‐and‐take recreational fisheries, fishes can be stocked at any size desired by Population dynamics in various stocking systems anglers and recaptured within days or weeks at the most. Such The population dynamics of stocked fisheries are influenced by fisheries can sustain very high catches without any biological size and density‐dependent processes. Natural mortality rates production. within fish populations are strongly size and age dependent, In stock enhancement, fishes are released into existing wild typically being orders of magnitude higher in early life stages populations. Stocking of early life stages or small juveniles prior than in adults and declining throughout the juvenile stages to the juvenile stages in which density dependence in survival is according to a fairly consistent allometric scaling (Lorenzen, strongest will elicit a strong compensatory response, often to the 2000). Compensatory density dependence is manifested mostly extent that stocking has no net effect on the abundance of larger in mortality in juveniles and in growth and reproductive varia- fishes but results in displacement of wild by hatchery fishes in bles in older fishes (Rose et al., 2001; Lorenzen, 2008a). While proportion to their relative densities at the stage of stocking density‐dependent mortality in juveniles exerts the strongest (Lorenzen, 2005). Releases of large juveniles after the life stages compensatory response in many fish populations, density‐ where density dependence in survival is strongest can raise dependent growth in older (recruited) fishes can also exert a abundance and biomass of large fishes beyond the level strong effect and sets the ultimate limits to carrying capacity supported by natural recruitment, but the extent of this will be (Lorenzen, 2008a). ultimately limited by compensatory growth responses The dynamics of culture‐based fisheries are driven entirely (Lorenzen, 2005, 2008a). Where the wild stock is fished within by stocking, harvesting and the mortality and growth processes sustainable limits, recruitment compensation implies that natu- that apply to the life stages represented in the stocked population. ral reproduction of released hatchery fishes will make at best a Management of freshwater fisheries: addressing habitat, people and fishes 573 small net contribution to natural recruitment while posing mortality rates of released cultured fishes are highly variable but potentially substantial ecological and genetic risks to wild stocks substantially higher on average than those of wild conspecifics of through replacement effects (Lorenzen, 2005). High and con- similar size (Lorenzen, 2000; Fleming & Petersson, 2001). tinuous releases may over time lead to complete replacement of Likewise, cultured fishes show lower r eproductive success than the wild by cultured or feral populations (Ford, 2002; Lorenzen, wild fishes (Fleming & Petersson, 2001; McGinnity et al., 2003). 2005). The empirical evidence for replacement of wild by Cultured fishes may also be more susceptible to capture by fish- released cultured fishes is variable and may reflect the interplay ing gear than their wild conspecifics (Mezzera & Largiadèr, of variable fitness of stocked fishes, duration of stocking, the 2001). Similarly, wild fishes not adapted to a recipient ecosystem habitat conditions of the recipient ecosystem and resilience of will often show low survival in the wild. the native stock to compensate for competition with stocked fishes (van Poorten et al., 2011). Because stock enhancements Genetic management can depress wild population abundance and also have deleteri- Three main sets of issues are associated with the genetic ous genetic impacts, it may be advantageous to separate cul- management of hatchery programmes: (1) potential disruption tured and wild population components as far as technically of neutral and adaptive spatial population structure due to possible. Releasing hatchery fishes as advanced juveniles translocation, (2) impacts of hatchery spawning and rearing (thus reducing interactions with wild juveniles at the stage on genetic diversity of stocked fishes and consequently when compensatory density dependence is particularly strong) after release on the enhanced, mixed stock and (3) impacts of and selective harvesting of hatchery fishes, possibly combined hatchery rearing on the fitness of released fishes and their natu- with manipulations to induce sterility, can greatly reduce rally recruited offspring. Wild fish populations show spatial ecological and genetic interactions with wild fishes (Utter, 2004; structure in selectively neutral markers where isolation has Lorenzen, 2005). been sufficiently strong and long term (Utter, 2004). Hatchery Restocking is normally considered only for populations that practices should reflect and maintain this structure by using have been depleted to a low fraction of their carrying capacity. brood stock of local origin where possible and through In this case, compensatory density‐dependent responses are appropriate brood stock management (Verspoor, 1997). Not expected to be weak until the population rebuilds substantially, doing so has been shown to carry substantial penalties in terms and even the stocking of early life stages may contribute to a of post‐release fitness, with implications for both enhancement net population increase. Populations that are at a low fraction effectiveness and risks to the wild population (Araki et al., of carrying capacity (depensation does not occur more difficult to avert than loss of diversity. Measures aimed at and thus kick‐start population recovery. minimizing fitness loss include rearing in near‐natural envi- In supplementation programmes for populations that are ronments, minimizing time in captivity, partially replenishing very small in absolute terms, dynamics are similar to those brood stock with wild fishes in regular intervals, equalizing described for stock enhancement, but release of additional family size or fragmentation of brood stock to reduce potential fishes may be beneficial by reducing the threat of extinction due for adaptation (Araki et al., 2008; Frankham, 2008; Lorenzen to demographic stochasticity despite eliciting a partial compen- et al., 2012). Reduced fitness of cultured fishes reduces the satory response (Hilderbrand, 2002). effectiveness of enhancements but still poses risks to the wild population component, which are greatest when fitness is only Aquaculture production of seed and domestication moderately compromised (Lorenzen, 2005). Several excellent effects guidelines and policies have been developed for genetic man- Rearing of fishes in hatcheries and other culture facilities s ubjects agement of enhancements, including Miller and Kapuscinski the organisms to an inadvertent or intentional process of (2003) and Tringali et al. (2007). domestication. Domestication processes occur inadvertently when fishes are brought into captivity but may be enhanced Interspecific interactions and ecosystem effects through measures such as selective breeding (leading to fully Interspecific interactions and ecosystem effects of stocking‐ domesticated fishes) or reduced by measures such as habitat based fisheries enhancement and restoration can arise through enrichment or life skills training aimed at producing more wild‐ various biological or technical means. Intensive interspecific like fishes (Lorenzen et al., 2012). As a result, cultured fishes biological interactions can arise where released fishes increase released into the wild tend to differ from their wild conspecifics the abundance of existing wild populations or establish new in a wide range of morphological, behavioural, physiological and populations where the species was previously absent. In either ecological attributes, which can lead to poor fitness (Sosiak et al., case, the strongest impacts on other fish species are likely to 1979; Ersbak & Haase, 1983; Olla et al., 1998). Indeed, natural arise due to predation from stocked piscivores or due to b iogenic 574 Fisheries development habitat modification by stocked species that may, for example, unintended consequences such as an increase in fishing p ressure reduce macrophyte abundance or increase turbidity (FAO, 1999; on wild stock components (Hilborn & Eggers, 2000). Such Eby et al., 2006). Interspecific competitive interactions for food responses may be used purposefully in recreational fisheries tend to be weaker but may also be significant (Levin & Williams, where increasing fishing effort and related economic benefits 2002). Impacts of stocked non‐native species are widely may be a key management objective (Loomis & Fix, 1998). perceived as a more serious threat to native biota than the Lastly, initiation and successful maintenance of enhancements release of native species. While non‐native fishes undoubtedly depend on governance systems that allow for regulation of have contributed to threats and extinctions of native fishes, the resource use and ensure that benefits of enhancements accrue to majority of non‐native fishes have integrated into existing com- those bearing the costs (Lorenzen, 2008b). munities without causing extinctions or even drastic changes in the abundance of native species (Moyle & Light, 1996; Keys to securing additive effects of stocking Williamson, 1996; Gozlan, 2008). Hybridization between closely Based on the background information examined, five key related cultured and wild species has been shown to occur and considerations are finally outlined that may be considered to can contribute to loss of genetic integrity and fitness of the wild increase the chances of generating additive effects of stocking. population (Hitt et al., 2003). Both competitive interactions and Firstly, stocking is most likely to generate positive fisheries hybridization may be particularly prevalent where the stocked outcomes whenever competition with wild recruits is low or even and wild species are closely related. When considering species absent due to reproduction failures. Otherwise, stocked fishes for stocking, it is therefore important to weigh the relative risks will compete with wild fishes and may partially replace wild of intraspecific interactions of stocking native species versus fishes unless the latter are competitively superior, which is often those of interspecific interactions associated with stocking and the case. Secondly, stocked fishes have to be properly adapted to introduction of non‐native species. cope with environmental challenges and natural selection pressures, which involve ecological and genetic ad aptation to condi- Diseases tions in the wild. Thirdly, additive effects are more likely when Impacts on wild stocks from diseases introduced by or with the predation burden is low and stocked fishes survive at high rates. stocking material may occur via three mechanisms: (1) introduc- Elevated survival can be achieved by stocking large‐bodied indi- tions of alien pathogens, (2) transfer of pathogens that have viduals that face lower predation losses. And finally, even the best evolved increased virulence in culture and (3) changes in host adapted and prepared fish has to be released into the wild while population density, age and size structure or immune status that minimizing transport and release‐related stress risks. Otherwise, affect the dynamics of established pathogens. Introductions of immediate losses to predators in the wild are very high. Because alien pathogens are associated with the most dramatic disease of the complexity of considerations, the reality of many stocking impacts of stocked on wild fishes so far documented (Johansen et programmes is that they have to be ideally conducted as experi- al., 2011). Controlling parasites in cultured fishes is crucial to mental releases using an adaptive management framework to minimizing disease interactions with wild fishes, but is not always learn the system‐specific responses. Such approach is highly effective and may not be sufficient, particularly where parasite advisable before large investments into hatcheries or similar transmission from wild to cultured fishes is difficult to avoid. It is infrastructure happen that are difficult or impossible to reverse. therefore important to implement an epidemiological, risk‐based We argue strongly against using stocking as a fix to environmen- approach to managing stocking‐induced disease transmission tal change or as a habitual practice because of the economic and that accounts for ecological and evolutionary dynamics of trans- ecological risks that such programmes carry. mission and host population impacts (Bartley et al., 2006).

Human dimensions Concluding remarks Human dimensions, the motivations, attitudes and behaviours of fishing stakeholders and the governance arrangements in The old adage that fisheries management is as much people as place to regulate the enhanced fisheries can have major implica- fish stock management is particularly true in the many small‐ tions for management outcomes (Lorenzen, 2008b). Three scale freshwater fisheries. This is because of the multi‐use issues shall be mentioned here. Firstly, it is usually stakeholder patterns characteristic for most freshwater ecosystems where needs that demand and justify stocking programmes (van local inland fisheries are social–ecological systems nested within Poorten et al., 2011). Moreover, many stocking programmes are other regional social–ecological systems and sectors such as agri- user financed through licence fees, for example, in angling culture. Because of resulting tight cross‐scale interactions among clubs. Stakeholder desires may also result in illegal translocation systems, sustainable inland fisheries are heavily dep endent on of fishes, which contributes to spread of non‐native fishes decisions made elsewhere with respect to water management, (Johnson et al., 2009). Secondly, individual and collective flood control, hydropower and navigation. Therefore, within responses of fishers to an enhancement programme may have the details of planning and implementing particular fisheries Management of freshwater fisheries: addressing habitat, people and fishes 575 management interventions such as harvest regulations or the Araki, H., Berejikian, B. A., Ford, M. J. & Blouin, M. S. (2008). Fitness type and amount of stocking, the fishery manager must ensure to of hatchery‐reared salmonids in the wild. Evolutionary Applications be well represented in all external decisions that spill over to the 1, 342–355. quality of the fishery. Unfortunately, with few exceptions (e.g. Arlinghaus, R. & Krause, J. (2013). Wisdom of the crowd and natural North American Great Lakes), inland fisheries are often margin- resource management. Trends in Ecology and Evolution 28, 9–11. Arlinghaus, R. & Mehner, T. (2003). Management preferences of urban alized in the wider freshwater ecosystem management and suffer anglers: habitat rehabilitation measures versus other options. Fisheries from low s ociopolitical priority that reduces political and admin- 28, 10–17. istrative support (Arlinghaus et al., 2002). Therefore, an inclusive Arlinghaus, R., Mehner, T. & Cowx, I. G. (2002). Reconciling traditional planning and management approach that integrates fisheries inland fisheries management and sustainability in industrialized within the broader scope of aquatic ecosystem management is countries, with emphasis on Europe. Fish and Fisheries 3, 261–316. often needed for sustainable inland fisheries. The reader is Arlinghaus, R., Cooke, S. J., Lyman, J., Policansky, D., Schwab, A., Suski, directed to relevant sources that outline elements of an integra- C., Sutton, S. G. & Thorstad, E. B. (2007). Understanding the com- tive approach to inland fisheries planning and management plexity of catch‐and‐release in recreational fishing: an integrative (Cowx, 1998; Lorenzen, 2008b). A range of more specific studies synthesis of global knowledge from historical, ethical, social, and bio- may also provide concrete guidance for deciding about the logical perspectives. Reviews in Fisheries Science 15, 75–167. concrete fisheries management actions that have been outlined Arlinghaus, R., Matsumura, S. & Diekmann, U. (2010). The conservation and fishery benefits of protecting large pike (Esox lucius L.) by harvest regula- in this chapter (e.g. introduction of fishes: EIFAC, 1988; tions in recreational fishing. Biological Conservation 143, 1444–1459. Welcomme, 1988; fish stocking: Cowx, 1994; Welcomme, 2001; Ashley, K. I. (1985). Hypolimnetic aeration: practical design and Arlinghaus et al., 2002; harvest regulations: Johnson & Martinez, application. Water Research 19, 735–740. 1995; FAO, 2012). Bain, M. B. & Stevenson, N. J. (1999). Aquatic Habitat Assessment: Common Methods. Bethesda, MD: American Fisheries Society. Bartley, D. M., Bondad‐Reantaso, M. G. & Subasinghe, R. P. (2006). A risk Acknowledgements analysis framework for aquatic animal health management in marine stock enhancement programmes. Fisheries Research 80, 28–36. Work on this chapter was supported by the German Federal Beam, J. H. (1983). The effect of annual water level management on Ministry of Education and Research (BMBF) within the pro- population trends of white crappie in Elk City Reservoir, Kansas. ject ‘Besatzfisch’ (www.besatzfisch.de) in the Program for North American Journal of Fisheries Management 3, 34–40. Social‐Ecological Research (grant no. 01UU0907) (R.A.). Beard Jr, T. D., Cox, S. J. & Carpenter, S. R. (2003). Impacts of daily bag Further support came through the EU FP7 REstoring rivers limit reductions on angler effort in Wisconsin walleye lakes. North American Journal of Fisheries Management 23, 1283–1293. FOR effective catchment Management (REFORM) project Bednarek, A. T. (2001). Undamming rivers: a review of the ecological (I.G.C.) and Federal Aid in Sport Fish Restoration grant impacts of dam removal. Environmental Management 27, 803–814. F‐135‐R (K.L). R.A. thanks Daniel Hühn, Thilo Pagel, Beklioglu, M., Carvalho, L. & Moss, B. (1999). Rapid recovery of a shal- Christian Wolter and Thomas Klefoth for discussions that low hypertrophic lake following sewage effluent diversion: lack of sharpened some of the material presented in this chapter. The chemical resilience. Hydrobiologia 412, 5–15. chapter was initiated while R.A. was on sabbatical leave at the Berkeley, S. A., Hixon, M. A., Larson, R. J. & Love, M. S. (2004). Fisheries University of Florida in the Fisheries Program. 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